An amino acid has been found on a comet for the first time, a new analysis of samples from NASA's Stardust mission reveals. The discovery confirms that some of the building blocks of life were delivered to the early Earth from space.

Previously, researchers have found amino acids in space rocks that fell to Earth as meteorites, and tentative evidence for the compounds has been detected in interstellar space. Now, an amino acid called glycine has been definitively traced to an icy comet for the first time. [...]

The researchers spent two years trying to find out - a painstaking task since there was so little of the comet dust to study. In fact, there was not enough material to trace the source of any compound except for glycine, the simplest amino acid.

"It's a great piece of laboratory work," says Lunine. "It's probably something that couldn't have been done remotely with a robotic instrument - it points to the value of returning samples."

Amino acids are easy to create in a random process. Throw together a sealed glass container of chemicals vaguely resembling the atmosphere of primordial earth, zap enough lightening through it - and you are likely to get some. c.f. the Miller-Urey experiment.

This (comet) result really has nothing to do with "panspermia" hypotheses and plenty to do with the stochastic properties of certain elements found in abundance under a wide range of realistic conditions.

I like (hence recommend) the "Recent Related Studies" section of the linked Wikipedia article.

Yeah, I read the original article and wondered what it was supposed to prove. So amino acids can form in space. Big deal. They can form spontaneously on earth too.

I would be way more impressed if they found solid evidence of any organized biological processes, even if they were ancient.

In fact I wish they had found something other than glycine, because that's the only amino acid that isn't optically active. All known life on earth (unless I am behind in the news) use only the levorotary enantiomers of the amino acids. That's important because in the Urey-Miller experiment you get a 50/50 mix. An uneven (or even solitary) combination would suggest some active process. But if all they found on the comet is glycine, there's no way to tell.

I had to look up several words but in the end that makes some sense. Lemme make sure I understand something, ok?

Some of the various amino acids struck by a photon reflect it, in some direction, phase shifted 90 degrees one way or the other. Glycine isn't one of those. You could say that some rotate the phase left, and others right.

Life on earth uses amino acids that rotate to the "left". Exclusively.

If you randomly create amino acids as in Miller-Urey, you get a gaussian mix of left-bending vs. right-bending amino acids.

If space amino acids had some deep connection to life on earth, you'd hope to find a comet with a noteworthy excess of left-bending amino acids.

Yes?

My question is: why in the world is the "left-bending" prejudice of life on earth? Does life *roughly* like ours have to be all left-bending amino acids or right-bending amino acids but not some random mix? Why?

That's basically it. You're asking the right questions. I don't think anyone knows for certain why life on earth only uses one form. I don't know of a reason why it's fundamentally necessary except that all of our cellular machinery and genes are programmed to use them and make them; there's no changing that now.

Some other hypothetical form of life might use the D forms, or both. The presence of both in equal proportions someplace wouldn't tell us anything about whether there is life, but finding one exclusively would be mighty interesting.

Anyway, if we ever figure out the reason, the next question is why all life on earth uses only the D (right-handed) form of the carbohydrates. Nobody has a good answer for that either!

Probably more [obvious], but remember that different rotary configurations have different chemical properties (as far as what can bond where how) and thus different biological ones. The optical properties are just one way to detect them. Demonstrative examples from pharma:

I'm not sure about the basis for the amino-acid preference, but it probably has something to do with an early useful enzyme appearing in that configuration, and/or perhaps the evolution of that same enzyme being favored by the configuration of DNA / RNA (if those came first, chicken and egg)...

First time I've heard of the carbohydrate thing (I should've stuck with biology...), but likely similar reasons - and then if the entirety of earthlife only uses the one configuration, there's no advantage to evolving mechanisms to handle the other, and probably breaks too many dependencies for it to survive as a mutation at this point. [Well, something simple like bacteria should have the option of pulling it off.. it'd be a fun engineering project to see whether there are any particular pressures against it with nucleic-acid-coded life.]

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So... I dunno if the point really needs clearing or not, but -- yeah, interesting, if a comet was full of amino acids and they all bent one way [whether the earth way or not], that'd suggest a complicated maybe-life-related origin, if Miller-Urey type nonlife-processes come out racemic.

But a racemic mix wouldn't totally rule out interesting origins, since we don't know that intergalactic pigeon shit doesn't come from intergalactic pigeons that are amino-acid-based but use both.

[We're just prone to look for earthlike stuff because we're proof that the Earth method succeeded at making things that do interesting stuff like move and eat and post to Livejournal once.]